1. Field of the Invention
The present invention is directed to acoustic stringed musical instruments, specifically, guitars and other hollow body instruments with fretted necks.
2. Description of the Related Art
Guitars and other fretted neck stringed instruments, unlike bowed stringed instruments, have the inherent trait of not having consistent intonation the full length of their neck, or fretboard. This being due to a guitar's various notes are dictated by the placement of its frets. These fret placements are chosen using the principle of harmonic equal temperament, and the strings behave under the properties of just temperament, This being caused due to the string to fret distance progressively increasing the length of the fret board. Being greatest at the higher registers. This increased string to fret distance compounds the tension of the string during the fingering of a note, therefore, slightly varying the pitch to a sharper value. The string height on guitars is referred to as; string action. Therefore, luthiers are forced to compromise between these two conflicting properties.
On acoustic guitars a negative neck angle of approximately 1 degree is desirable in order to maintain a slight string break angle at the bridge saddle, this being done for tonal and volume purposes. The height of the bridge saddle from sound board surface is also very specific for acoustic considerations.
It is paramount that the guitar neck to body joint and neck angle of inclination relative it's body top plate (soundboard) to be as perfect as possible, to achieve intonation as near perfect as possible at the desired string action.
Traditional acoustic guitars makers have always coupled the neck to the body using traditional wood working technics. Essentially, block to block joints: variations of mortis and tenon, dovetail, or combinations thereof. Bonded by gluing with/or by mechanical fastening (screws, etc.).
Most have employed a system where one half of the joint is on the neck, known as the heel, a carved wood block either glued or carved into the neck. Normally beginning at the twelfth fret and ending at neck to body junction, the fourteenth fret. The second half of the joint, known as a neck block, is located inside the body connected to the guitar rim adjacent to the neck. Heelless necks have also been used less frequently. In this joint the neck block inside the guitar is quite large and extends almost to the sound hole. A rectangular neck pocket is machined into the top of the guitar body and the neck tail is shaped such that it transcends from a rounded shape into rectangular at the fourteenth fret and drops into the pocket and is held in place by four long screws that pass through holes drilled in the back of the guitar
Another of luthiers' many considerations, when instrument building is bridge lift. When guitar strings are tuned to proper pitch the stress on the sound board at the string ends connection at the bridge results in a strain causing the sound board to convex upward, slightly, at the bridge region. The amount of this bridge lift is dependent upon the individual soundboard's stiffness, the stiffer the soundboard the less lift. With wood constructed guitars no two soundboards are identical, and have varying degrees of stiffness. Therefore, the actual bridge lift characteristics of each soundboard is only guessable but not absolutely predictable. The amount of bridge lift results in the equal variance in string height. The above is most problematic with steel string instruments, less so with nylon strung instruments and not at all in composite material constructed guitars. Higher end guitars sometimes require intensive labor reworking of the neck set-in before obtaining the desired string action height.
Wood guitars are susceptible to humidity, temperature, seasons, etc. And a guitar's action is in a constant state of wandering. Guitars require constant maintenance in this regards. Up to and including neck resets. Composite and other non-wood constructed instruments do not share these characteristics with wood guitars. Another phenomenon which occurs from the ageing of the guitar is that the various members, primarily, the sound board strain under the tension of the strings. And eventually, will become permanently fixed, in what luthiers call “creep”. Steel strings of thicker gage with their increased tension exuberates this problem. Over time, all acoustic guitars tend to hinge about the neck to body joint and to suffer from a rising soundboard. Under the continual strain from the string tension, the action height gradually increases and the guitar becomes less and less playable. With a traditional set neck, correcting this problem, by re-setting the neck, is a highly skilled and expensive business.
Guitar players and collectors, like luthiers, tend to be very traditional and understand that a highly crafted guitars are cherished and need periodic maintenance and happily care for such instruments. A great guitar is an art object.
Mass produced guitars, on the other hand, especially, entry level guitars where cost of production constants apply. The attention to a guitar's set-up and playability is little to nonexistent and resultant instruments playability are not consistent from one instrument to the next.
Throughout the history of the guitar up to the present, there have been hundreds of innovations regarding adjustable neck angle. Beginning in the early nineteenth century with luthier Johan Stauffer's hinged neck, adjusted by turning a square clock-key-style screw through a hole in the neck heel.
These innovations and apparatuses have relied upon modifications of the basic wood joints. with and without the employment of various adjustment components: screws, levers, shims, hinges, pivots, and various combinations thereof. A good system with a single simple adjustment, able to be done under tuned string tension and in the playing position as of yet, has not seen the marketplace.
Of benefit with a simple neck angle adjustment, would be in guitar manufacturing. Guitar builders who produce models with incorporated neck angle adjustment would have the advantage of easily and economically making fine adjustment in string action after production, resulting in excellent playability. Secondly, guitar players would have the option to adjust string action to their own personal preference. Ideally these adjustments would be simple and able to be done with the guitar strings under tuned tension.
The sector of the mass produced market is especially important because nearly all players learn on entry-level instruments, but unfortunately the quality of setup is often poor compared to instruments built by luthiers. Unfortunately beginners learn on the hardest to play instruments.
With composite material constructed guitars (synthetic, carbon fiber and/or reinforced plastic, etc.) are mostly molded as single tubs consisting of the bottom portions of the neck and body in one piece, minus neck headstock top panel, fretboard and soundboard panel. These panels are then bonded to the tub. Unfortunately this molded construction technic renders said instrument's set-up permanent and not modifiable without compromising other acoustic elements.